1. Field of the Invention
The present invention relates to a method of coating a lubricant in a metallic injection machine which comprises a stationary die and a movable die, and in which a cavity is formed on a side of a parting face of the dies, when the movable side die is fastened to the stationary side die, and a molten metal is injected from an injection nozzle to fill the cavity by way of filling holes of a sprue hole, a runner groove, a gate hole and the like, a metallic mold is provided, and a lubricant is coated on surfaces of the filling holes and a cavity of the die before injecting and filling the molten metal.
2. Description of the Related Art
There is known a thixotropic molding method as one of a molding method for providing a metallic product from a low melting point metallic material of an aluminum alloy, a magnesium alloy, a zinc alloy or the like. According to the method, when an alloy raw material is agitated in a solid/liquid coexistent state, formation of a dendritic crystal, that is, dendrite is restrained, a slurry-like substance brought into a state in which a broken small granular solid and a liquid are coexistent is provided, and the slurry-like substance brought into the solid/liquid coexistent state is injected into a die to solidify to provide a metallic mold having an alloy structure substantially uniformly distributed with the solid. By the method, according to the metallic mold, a shrinkage rate by solidification is small, microshrinkage, that is, a shrinkage hole and a cavity hole by entrapping with a gas is reduced and therefore, an excellent property is shown both in a dimensional accuracy and a mechanical property. An injection molding machine is also used for a method of producing such a metallic mold utilizing the property of the slurry-like substance. The injection molding machine is generally constituted by a heating cylinder, and a screw provided to be able to be driven in a rotational direction and an axial direction at inside of the heating cylinder. A front side of the heating cylinder is attached with an injection nozzle of an open type ‘plugged’ by a cold plug, or an injection nozzle provided with a shut off valve.
On the other hand, there is known a diecasting method of a hot chamber type as other method of producing a metallic mold. A diecast machine used in embodying the diecasting method is constituted by a stationary die attached to a stationary die disk, a movable die paired with the stationary die, an injection nozzle brought into press contact with the stationary die and the like. The injection nozzle comprises a sleeve, and a plunger provided to be able to be driven in an axial direction at inside of the sleeve. The sleeve is provided with a molten metal supply port. Further, a cavity for molding the metallic mold is formed at a parting line between the stationary die and the movable die. Therefore, when the movable die is fastened to the stationary die, the molten metal in a crucible is supplied into the sleeve by a predetermined amount from the molten metal supply port, the injection nozzle is brought into press contact with the die, and the plunger is driven, the molten metal is injected into the cavity. When the movable die is opened after awaiting for cooling to solidify the injected and filled molten metal, an ejector pin is projected to provide the metallic mold.
In order to provide the metallic mold by injecting the molten metal to fill in the cavity of the molding dies as described above, a lubricant of a liquid or a powder is coated on a surface of the cavity to facilitate to take out the metallic mold from the dies, or to avoid the molten metal from being brought into direct contact with the surface of the cavity. The lubricant is coated by opening the movable die from the stationary die, and directly spraying or coating a water-soluble lubricant constituted by diluting a lubricant solution by water by a spray apparatus. However, according to the principle of the coating method, the water-soluble lubricant is coated and therefore, there are indicated problems of lowering of a die temperature by water, a deterioration in a quality of the mold by scattering the water-soluble lubricant, a deterioration in an operational environment and the like.
Hence, there are proposed coating methods for coating the lubricant in a state of closing the dies. That is, JP-A-62-127150, JP-A-2001-113352 and JP-A-2004-167537 show a method of coating the lubricant by closing the dies and decompressing inside of the cavity, further, JP-A-7-323360 shows a coating method of closing the dies and pressurizing the lubricant into the cavity. Explaining further in details, the lubricant coating method shown in JP-A-62-127150 is applied to diecasting of a cold chamber type, in which the molding dies are closed, inside of the cavity of the dies is brought into a decompressed state by a sucking apparatus, thereafter, the lubricant is coated from a molten metal supply port of an injection sleeve. Further, JP-A-2001-113352 discloses a method of supplying a lubricant by compressed air from a side of a cold plug catcher to a cavity by decompressing inside of a sprue hole, a runner groove, a gate hole, the cavity and the like from the side of the cavity when the lubricant is coated in a die which comprises a stationary side die and a movable die, and in which the sprue hole, the runner groove, the gate hole, the cavity and the like are formed on a side of a parting face of the dies, and which is formed with the cold plug catcher communicated with the sprue hole.
JP-A-2004-167537 shows a diecast machine provided with a projecting pin for projecting a cast product from a die, and a lubricant supply apparatus. The projecting pin of the diecast machine is formed with a supply path for supplying a powder lubricant to a cavity. Further, when the powder lubricant is coated, the projecting pin is projected to shut off a molten steel path and when inside of the cavity is decompressed, the lubricant is coated by being borne on an exhaust air flow. Further, JP-A-7-323360 shows a lubricant coating apparatus of diecasting having an injection sleeve and a lubricant supply apparatus. A molten steel path opening/closing member is provided between the injection sleeve and the lubricant supply apparatus, when the lubricant is coated, a side of the injection sleeve is closed and when the molten steel is injected, the lubricant supply side is closed. Further, the lubricant is injected into the cavity by a pump. When injected, air in the cavity is exhausted by the injected lubricant.
According to the methods of coating the lubricant described in JP-A-62-127150, JP-A-2001-113352, JP-A-2004-167537 and JP-A-7-323360, in any of the coating methods, the lubricant is coated after closing the dies and therefore, the lubricant is not scattered to outside of the dies, the extra lubricant can be recovered by the sucking apparatus or a lubricant exhaust path and therefore, there are achieved advantages of capable of restraining a deterioration in the operational environment and also minimizing a reduction in a mold temperature by coating the lubricant. Particularly, according to the coating method described in JP-A-2001-113352, by decompressing insides of the sprue hole, the runner groove, the gate hole, the cavity and the like from the side of the cavity, the lubricant is coated from a side of a recess portion to the cavity and therefore, it is not necessary to move the injection nozzle at each time of coating the lubricant and therefore, a molding cycle is not prolonged, and the productivity is not deteriorated. Further, it is not necessary to move the injection nozzle at each shot and therefore, an excellent advantage that power cost is not increased is recognized.
However, according to the methods of coating the lubricant of the related arts, problems or points to be improved are also recognized. For examples according to the coating method described in JP-A-62-127150, it is anticipated that when decompressed by the sucking apparatus, in view of the structure of the injection apparatus, outside air invades from the molten metal port or a clearance between sliding faces of the injection plunger and the injection sleeve, and a high decompressing degree is not achieved. As a result, in molding a metallic mold having a thin wall thickness, a metallic having a long total length in a direction of flow of the molten metal, a pressure loss of the lubricant flowing in the cavity is large to bring about a case in which the lubricant cannot be coated sufficiently up to a distal end portion of the cavity. According to the invention described in JP-A-2001-113352, although a number of characteristics are achieved as described above, there is not adopted a significant measure with regard to a contact pressure for pressing the injection nozzle to the stationary die and therefore, there is a concern that a predetermined decompressing degree is not achieved by invasion of outside air when inside of the cavity is decompressed. Further, when the lubricant is supplied by compressed air, the lubricant cannot be supplied by high pressure and therefore, there can be a case in which the lubricant is not sufficiently supplied to corners of a narrow cavity or a cavity having a long flow length.
According to the coating apparatus shown in JP-A-2004-167537, when decompressed, the injection apparatus or the side of the injection nozzle is closed by an extruding pin, that is, a shut off mechanism and opened when the molten metal is injected. Thereby, although a desired vacuum degree is achieved, there pose problems that the die structure becomes complicated, a frequency of maintenance of the shut off mechanism portion is increased, opening/closing operation is needed and a molding cycle is prolonged and the like. According to the coating apparatus disclosed in JP-A-7-323360, the molten metal path opening/closing member is provided between the injection sleeve and the lubricant supply apparatus, when the lubricant is coated, the side of the injection sleeve is closed, when the molten metal is injected, the lubricant supply side is closed and therefore, although a desired vacuum degree is tentatively achieved, since the molten metal path opening/closing member is provided, a problem similar to that of the invention described in JP-A-2004-167537 is posed.
As described above, according to the lubricant coating methods or the die apparatus of the related arts the pressure at inside of the cavity cannot be maintained to the desired pressure and therefore, there is a concern that the metallic mold having the thin wall thickness, the metallic mold having the long total length in the direction of flow of the molten metal and the like cannot be molded. Further, according to the structure having the structure of capable of maintaining the pressure in the cavity to the desired pressure value, the metal path opening/closing member is provided to pose the problems of complicating the die structure, increasing the frequency of maintenance, needing the opening/closing operation, prolonging the molding cycle and the like.
The invention intends to provide a method of coating a lubricant in a metallic injection molding machine resolving the above-described problem or drawback of the related arts, specifically, it is an object of the invention to provide a method of coating a lubricant in a metallic injection molding machine capable of sufficiently coating a lubricant up to a distal end portion of a cavity to provide a metallic mold having a special shape such as a metallic mold having a thin wall thickness, a metallic mold having a long total length in a direction of flow of molten metal or the like. Further, it is an object thereof to provide a method of coating a lubricant in a metallic injection molding machine without particularly needing maintenance and without impairing an injection nozzle or a stationary side die with which the injection nozzle is brought into contact.